1. Field of the Invention
The present invention relates to a method of chemical vapor growing of a metal nitride film and a method of manufacturing an electronic device using the same and, more specifically, it relates to a method of chemical vapor growing of a metal nitride film which is nitrided thoroughly to contain less impurities and with less dust of side reaction products formed during film deposition, as well as a method of manufacturing an electronic device having an interconnecting layer using the same.
2. Description of the Related Art
Al series metals such as Al--Si have been generally used as internal interconnecting material for semiconductor devices such as ULSI (Ultra Large Scale Integrated Circuits) and various kinds of electronic devices. In recent years, as the design rule for the interconnections has required a finer level in the order of less than sub-quarter micron, and integration degree and performance have been increased, there are various problems such as lowering of working frequency due to increase in the resistance of interconnections, increase of electric power consumption and deterioration of resistance to various migration.
Accordingly, use of Cu series metal interconnections with less specific resistivity compared with Al series metals has been considered. The specific resistivity of Cu is 1.72 .mu..OMEGA..multidot.cm which is about less than 2/3 of 2.7 .mu..OMEGA..multidot.cm of Al. Further, the Cu metal interconnections have higher resistance to electro migration or stress migration than Al series metal interconnections.
As the method of depositing a Cu film, a well-known electric field plating method is generally employed, but the method requires to form a seed layer previously as an underlying conductive layer for the Cu film and involves a problem in view of the matching property with other dry processes.
In view of the above, it has been attempted a method of depositing a Cu film by a sputtering method or a CVD (Chemical Vapor Deposition) method.
It has been known that Cu metal interconnections are excellent in electric performance and migration resistance but the Cu metal atom itself easily diffuses into Si or SiO.sub.2. Therefore, in a semiconductor device, for instance, a barrier layer for inhibiting diffusion of the Cu atom has usually been formed prior to the formation of the Cu film on the underlying impurity diffusion layer, the lower interconnecting layer or interlayer insulation film.
Heretofore, TiN films have been used generally as a barrier layer for interconnections comprising high melting metals such as W and Al series metals. However, since a crystal structure grows in a columnar structure in the TiN film, it still leaves a possibility of diffusion of metal atoms along the grain boundary and the function as the barrier layer is not satisfactory for Cu atoms which diffuse more easily than Al atoms or W atoms.
Then, as a material for the barrier layer effective to the Cu metal film, TaN, W.sub.2 N, Ti--Si--N, W--Si--N, Ta--Si--N and the like have been noted. Since the materials described above have an amorphous structure, grain boundary diffusion is less likely to occur compared with a TiN film.
In actual semiconductor devices, since it is applied as a barrier layer in a connection hole (contact hole and via hole) at a high aspect ratio in a multi-layered interconnection structure, deposition of a TaN film, W.sub.2 N film, Ti--Si--N film, W--Si--N film, Ta--Si--N film or the like by the CVD method, which is excellent in step coverage over the sputtering method, has been attempted.
As starting gases used in CVD for the metal nitride films, those exemplified in Table 1 are typically used.
TABLE 1 Metal Nitride Starting gas TaN TaBr.sub.5 + NH.sub.3 W.sub.2 N WF.sub.6 + NH.sub.3 Ti-Si-N TiCl.sub.4 + NH.sub.3 + SiH.sub.4 W-Si-N WF.sub.6 + NH.sub.3 + SiH.sub.4 Ta-Si-N TaBr.sub.5 + NH.sub.3 + SiH.sub.4
The metal nitride films are deposited by the thermal CVD method using the starting gases exemplified in Table 1, and fine solid particles of ammonium halide such as NH.sub.4 Cl or NH.sub.4 F are formed as side reaction products. Further, when SiH.sub.4 is used as a portion of the starting gases, fine solid particles containing Si are also formed in a gas phase. Such fine solid particles result in a problem that they remain as a great amount of dust in a CVD chamber or on a substrate to be processed.
For avoiding the problem of dust caused by ammonium salts, it has also been attempted to use N.sub.2 or NF.sub.3 as shown in Table 2 instead of NH3 as a nitriding gas. In this case, since it is difficult to thermally dissociate N.sub.2 or NH.sub.3, a plasma CVD method is employed.
TABLE 2 Metal Nitride Starting gas TaN TaBr.sub.5 + N.sub.2 + H.sub.2 W.sub.2 N WF.sub.6 + NF.sub.3 + H.sub.2 WF.sub.6 + N.sub.2 + H.sub.2
However, in RF (13.56 MHz) plasma discharge, for example, by a usual parallel plate type plasma CVD apparatus is insufficient for reducing metal compound gases, namely, metal halides in this case and halogen atoms remain in the resultant deposition films being bonded with metal atoms. Therefore, metal atoms and nitrogen atoms in the deposition film can not form firm bondings. Accordingly, in the heat treatment of the step after the formation of the barrier layer, nitrogen atoms diffuse externally from the barrier layer to bring about a worry of degrading the barrier property to Cu metal interconnections or the like.